1. Field of the Invention
The present invention relates to a laser cutting machine and specifically to light sensors used for focusing, cutting fault detection, and the like.
2. Description of the Background Art
In a laser cutting machine for cutting a workpiece with a laser beam, the cut state of the workpiece must be monitored continuously in order to reduce the time of piercing conducted at the start point of cutting, to prevent blow-up during piercing and to prevent a cutting fault, e.g., gouging, burning or dross sticking. For this purpose, an apparatus is required for detecting and monitoring a beam generated on the cut surface of the workpiece during cutting.
FIG. 29 shows a visible light detector apparatus for use in a conventional laser cutting machine disclosed, for example, in Japanese Laid-Open Patent Publication No. HEI4-91880 or in Japanese Laid-Open Patent Publication No. HEI4-105780. In this drawing, the numeral 1 indicates a light sensor using a photoelectric device or a camera device, 2 denotes a cutting head, 3 designates a cutting lens, 4 represents a nozzle, 5 indicates a mirror for reflecting a light from a cut surface in the direction of the sensor, 6 designates a window provided in the cutting head 2, 7 represents a detection section for judging piercing completion, a cutting fault and the like based on the light detected by the light sensor, 8 denotes a laser beam, 9 indicates a light from a workpiece, 10 represents an NC apparatus, 11 denotes a bend mirror, 12 designates a laser oscillator, and W indicates a workpiece.
In the conventional laser cutting machine constructed as described above, when the workpiece W is irradiated with the laser beam 8, part of a light generated on the cut surface due to the fusion or the like of an irradiation point is reflected by the mirror 5 and received by the light sensor 1. The change in intensity of such light is detected by the light sensor 1, piercing completion timing or cutting fault occurrence is detected by the detection section 7, and this information is transmitted to the NC apparatus 10 to control the laser cutting machine.
In the aforementioned conventional laser cutting machine, the mirror and sensor fitted to the cutting head adjacent to the workpiece may interfere with the operation of the machine and may be contaminated by fumes and/or spatter produced by the workpiece during cutting, or may be damaged by the scattered light of the laser beam. Such effects make the stable long-time operation of the machine difficult. Also, since the mirror must be disposed in a position where it is not exposed to the laser beam, typically the top, the cut area cannot be viewed from that convenient perspective. At other viewing positions, there may be an insufficient quantity of light, resulting in a low detection sensitivity, a difficulty in obtaining the real image of a cut point, and an insufficient amount of operational data. Further, if the cutting head contains the sensor, all cutting heads which may be used in the cutting operation must be equipped with a sensor mechanism, thereby resulting in a high price.
It is, accordingly, an object of the present invention to overcome the disadvantages in the conventional designs by providing a low-priced laser cutting machine which allows stable operation to be performed for a long time, the real image of the cut point to be obtained, detection sensitivity to be high, and only one sensor mechanism to be required for the apparatus.